This invention relates to cleaning systems.
More particularly, the present invention relates to differential physical chemical cleaning.
In a further and more specific aspect, the present invention concerns ionic sponge materials and a method of producing the same used in differential physical chemical cleaning systems for cleaning hydrophobic surfaces.
Many industries today require the ability to efficiently clean highly finished surfaces, removing particles and other surface contaminants. Specific articles having highly finished surfaces include, but are not limited to, wafers of semiconductor material, and memory disks.
Semiconductor wafers must be cleaned prior to any processing steps used to produce semiconductor devices. Due to the fragile nature of semiconductor wafers, achieving a high degree of cleanliness, as well as a high yield of clean wafers is difficult. Many cleaning devices produce a low yield of clean wafers due to breakage or an unacceptable level of surface contaminants. Memory discs provide less of a problem with breakage, being more durable.
Currently, cleaning devices have been developed to overcome some of these problems. Devices for cleaning wafers generally consist of a cylindrical roller passing over a wafer. The cylindrical roller conventionally includes tufted nylon or other types of bristles extending from a central core. The bristle roller brushes are fixed horizontally and rotate as the wafer or memory disk is passed between the bristle surfaced brushes while the surfaces are copiously drowned in cleaning solution or de-ionized water.
Wafers cleaned in this manner are often unacceptable due to particles and other surface contaminants missed or passed over in the cleaning process. In addition, the softness of the bristles varies according to their composition, resulting in a heterogeneous mixture of bristles, each harder or softer than their counter parts. This results in breakage of the wafers as well as damage to wafer surfaces. Other drawbacks, resulting in unsatisfactory cleaning, may be attributed to the hydrophobic nature of bristle tufted brushes. The fiber surfaces of these brushes are never wetted, and require large amounts of de-ionized water or cleaning solution to work in the cleaning process.
Substantially more effective, are roller brushes formed from sponge material. Typically, roller type cleaning devices employ an outer layer of sponge material. While cleaning devices employing sponge material are effective in generally cleaning a surface by removing a great deal of particulate material and other surface contaminates, they are less effective in removing fine particles to provide a more extensively cleaned surface.
These mechanical scrubbing devices, however, are still deficient in their ability to clean the surfaces. The mechanical cleaning of wafers, memory discs and other electronic materials and substrates is deficient because substantially complete cleaning takes place at the molecular level and not at the mechanical level. Ultra-fine particles adhere to the surfaces of substrates by mechanical means and more importantly, by electrostatic forces. Attempting to remove these particles by mechanically washing the surface with brushes and conventional sponge material is often futile. When the size of a particle approaches sub-micron and amicron sizes, they take upon themselves a formal charge which is held to a hydrophobic surface by what is described as electrostatic or van der Waals forces. This well known phenomena is observed in many aspects of wafer and memory disk processing.
Removal of electrostatically attracted particles is almost impossible by conventional means. Various claims have been made that removal of ultra-fine particles can be achieved solely by controlling the porosity of micro-porous sponge devices used in the cleaning process. This cannot be substantiated, since cleaning of a hydrophobic surface entails many variables such as water pressure or solvent volume, forces applied upon the surface, surfactants and their polarity, interface relations between the hydrophobic surface and the hydrophilic surface and a host of physical/chemical variables. Therefore, conventional cleaning devices cannot provide the close cleaning a finely finished surface requires.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Accordingly, it is an object of the present invention to provide a new and improved sponge material.
Another object of the present invention is to provide an improved method of cleaning surfaces of articles.
And another object of the present invention is to provide an improved method of producing sponge material.
Still another object of the present invention is to provide a sponge material capable of removing ultra-fine particles including sub-micron and amicron sizes, from hydrophobic surfaces.
Yet another object of the present invention is to provide a sponge material capable of attracting charged particles.
Yet still another object of the present invention is to provide a cationic sponge material.
A further object of the present invention is to provide a system for removing undesirable particles.
And a further object of the present invention is to provide a material capable a attracting undesirable particles.
Briefly, to achieve the desired objects of the present invention in accordance with a preferred embodiment thereof, provided is a differential physical chemical cleaning system including a plurality of formally charged cleaning devices for engaging a surface to be cleaned and a fluid delivery system for delivering precipitating agents to the surface to be cleaned and the plurality of cleaning devices.
Further provided is an ionically charged sponge material for attracting and for retaining charged particles. The sponge material includes a plurality of ionic hydroxylated polymers cross-linked to a plurality of hydroxylated polymers.
The ionic hydroxylated polymer preferably includes cationic polyvinyl alcohol wherein the cationic polyvinyl alcohol includes formally cationically charged atoms.
Further provided is a method of forming cationic sponge material including the steps of forming a plurality of cationic hydroxylated polymers, forming a plurality of hydroxylated polymers, and cross-linking the cationic hydroxylated polymers and the hydroxylated polymers.
In a more specific method the step of forming the plurality of cationic hydroxylated polymers includes the step of forming an epoxide and reacting it with polyvinyl alcohol. Forming an epoxide includes reacting a quaternary ammonium complex with a metallic hydroxide.
Also provided is an ionically charged material for attracting and for retaining charged particles including a plurality of cross-linked hydroxylated polymers, a host molecule cross-linking the hydroxylated polymers, and a guest molecule having a high charge density carried by the host molecule.